Method of improving the utilization of the heat energy produced in a wood grinding process

Abstract

A method of improving the utilization of the heat energy produced in a wood grinding process when wood is ground in a grinding space (3) under a pressure exceeding atmospheric pressure, and warm shower water (G) is sprayed into the grinding space. Steam (H) is separated from the groundwood pulp (A) discharged from the grinding space in a steam separator wherein the groundwood pulp is allowed to expand from its inlet pressure to atmospheric pressure in at least two steam separators (11,14) by releasing steam from the groundwood pump in each steam separator by decreasing the pulp pressure. The amount of steam (H1,H2) released in the separate steam separators is adjusted according to the proportions in which steam is needed for utilizations purposes. Thus the heat energy of the pressure grinding process can be recovered in separate steam fractions the amount and pressure of which correspond to the requirements of the utilization purposes. It is preferable to heat the shower water by steam of such a volume and pressure that the temperature of the shower water increases to a desired degree, preferably above 100° C.

What we claim are: 
     
       1. A method of improving the utilization of the heat energy produced in a wood grinding process of the type in which wood is ground by means of a rotating grinding member in a grinding space under superatmospheric pressure while warm shower water is sprayed into the grinding space, and the groundwood pulp is fed from the grinding space into steam separator means wherein the heat energy contained in the groundwood pulp is released in the form of steam, which method is characterized by the fact the groundwood pulp discharged from the pressurized grinding space is allowed to expand from its inlet pressure to atmospheric pressure in at least two steam separators by releasing steam from the pulp suspension in each steam separator by lowering the pressure therein, and that the temperature and pressure of the steam released from each steam separator is adjusted to correspond to steam utilization needs, the groundwood pulp being allowed to expand in the steam separators to such an extent that the pulp suspension temperature is decreased in the last steam separator to about 100° C. 
     
     
       2. A method according to claim 1, in which pressurized steam released in the steam separators is used for heating the shower water to be fed into the grinding space. 
     
     
       3. A method according to claim 2, in which released steam of a pressure above atmospheric pressure is used to heat the shower water to a temperature preferably exceeding 100° C. 
     
     
       4. A method according to claim 2, in which released steam of atmospheric pressure is used to heat the shower water. 
     
     
       5. A method according to claim 2, in which the steam is fed directly into the shower water. 
     
     
       6. A method according to claim 1, in which the groundwood pulp is allowed to expand in at least three steam separators, and steam for heating the shower water is released at the earliest from the second steam separator.